Of course 60,000 psi is high, although many of us think it is not Danger High. The barrel does not have any problems at these pressures. The .284 specs are 63,000 psi and that includes mountain barrels that have the same chamber dia as does the 450b and then gets smaller than the 450b out to the muzzle. Also consider the 460 S&W’s pressures which are in the 60,000 arena. Which do you think is more durable the S&W or an AR? However, having said all this, I would not try to load for 60,000, until you become much more experienced. The only real consideration is bolt thrust. The .223 psi. spec. is for 52,000 psi and if one were to load the 450b for this spec, the bolt thrust will be way lower than the .223’s, as per the copper crusher studies as sited by Wayne State University and re-quoted in the gun rags. These were studies done with a special copper crusher placed on the bolt face and then firing the cartridges, so as to compare the 223 to the 45Pro. This was done after they realized that the standard bolt thrust formulas did not apply. I suppose they had to re-learn the principal that bottle necked cartridges have much more thrust. So, maybe this will be over simplified, but in the example of the 450b, not any other AR cartridges, if you have enough wall thickness in the chamber and have a straight case, one can indeed pump up the pressures and stay in the safety margins. That’s the trick, safety margins. The arm chair warriors will do all the nay-saying and because they cannot do it, then neither can you, but I tell you this, it takes guys like you, with the guts, to find out that there are paradigms’ out here and were all along, that are being broken and will yet be broken.
PS. Try sizing the Hornady 350gr. 458 bullet to 452. You are only shrinking them down .003″ per side (less than half the size of a human hair) and doing this with other similar bullets has not shown jacket problems in flesh. I don’t think this will work with copper/brass solids; of course this trick is only if you just have to have heavy bullets and want to fully realize the full potential of the 450b. Good luck.